I haven't taken a written music theory exam, and I never will, but I don't understand how it would work. You've got a lot of people in a room, all trying to answer the same questions. And if half of them are like me, then half of them are humming or whistling in order to figure out if this passage sounds major or minor, or what the underlying chords are, or whatever. That's how I work and I would find any other technique much harder. Judging by their recordings, I think Thelonius Monk and Glenn Gould feel the same way, so I'm definitely not alone. So I imagine a cacophony of people all doing this at once, distracting each other. Is that what it's like, or do you have to remain quiet, or what happens?
One of the goals of music theory is to be able to tell whether a passage is major or minor and to completely analyze without needing to hum or whistle at all.
Cadences often have to be heard, though. In the class I took where score analysis required finding cadences, our professor set aside a portion of the exam time for playing recordings of the excerpts in question. No humming needed.
Note that in American university ear training courses, humming is generally prohibited but overlooked if done quietly by beginners. By the third semester the expectation is that students can audiate, that is hear the music completely in their heads right from the page. During sight singing juries, points may be deducted for any noises made before beginning the excerpt.
I've taken a fair number of classroom music theory exams, and they were generally quiet. Any humming would have been done very, very quietly.
But since the exams are primarily analytical, there's also an expectation that they'll be answered near entirely by analysis.
Theory curricula are often combined with ear training and rhythm training. Those exams are typically done separately and individually.
I see what you're getting at! But no, theory exam rooms are generally pretty quiet.
Here's the sort of thing you're asked to do. (Grade 5 is the 'everyone needs to know this much' level.)
Generally, written music exams are silent, just like any other exam. The extent of permitted humming or quiet whistling is generally up to the examiner and governing body.
Some other types of exams are taken using computers, which may include audio components with headphones.
Performance-based examinations are necessarily different.
People with the Aphantasia condition (about 4% of the population) have limited sensory recall/imagination, varying in degree and type. For those with audio aphantasia, exam conditions can be very challenging indeed.
Just to clarify the kind of "music theory exam" we're talking about, this does NOT include "ear training" / "aural test" which @AndyBonner described well in his comment:
(To elaborate: "ear training"/"aural skills" exams necessarily have out-loud content. Anything requiring the student to listen—like, to hear and write down melodies or chords—can be administered to a whole class at once, but anything requiring the student to "perform," like to sing a melody using solfege, has to be done in private with one student at a time to avoid students "getting the answer" from others' performances. In my undergrad, these skills were actually a separate course from music theory classes and had their own exams.)
@Laurence's answer provided a sample ABRSM grade 5 exam where the only possible benefit from humming comes in section 5 (chords) but you can mitigate by visually counting the steps in the ledger lines between the notes.
In higher grades, like this grade 8 exam, you need to do:
- some simple composition (example: Section 1.1 and 2.1),
- harmonization (example: Section 4.1, also this ABRSM Grade 8 Trio Sonata question), and
- analysis (example: Section 5)
where humming or playing the score on the keyboard would have been helpful. BUT THEN, as you advance in your training, you are ALSO expected to be more proficient in hearing the music in your head, although not to the extent that Beethoven was able to do when he became deaf.
I admit that when I took those ABRSM exams, as well as college level ones, I sometimes wish that the exam room would provide a keyboard with headphones for anyone to use during the exam, but alas, it's not provided. I think it's part of the training to be able to do all those tasks in your head. My fellow exam takers and classmates have been absolutely courteous to maintain a quiet environment like in the library.